During single player mode, you can get more firepower and more lives by setting the controls of both players to be exactly the same. For example, player one - Fire=Space and player two Fire=Space. By doing this, you can focus on one blob, but the other blob will move with and shoot with you. This kills more enemies and gets you to higher levels. A great idea is to set the special key to a different button for each player so that you can get double the cow bombs.